There are many suture anchor designs on the market today intended to secure suture, which is passed through soft tissue, to bone. Most pre-loaded suture anchors require tying a knot to secure tissue in place. Knot-tying is time-consuming, prone to technical failure, and may lead to abrasion of the underlying tissue as a result of the mass effect of the suture knot. The preferred method is moving toward using anchors that do not require tying knots in the suture to secure the tissue against bone. Use of a knotless suture anchor construct saves time, requires less technical expertise, and avoids the potential mass effect of a suture knot on the underlying tissue. Also, the knots have been shown to be a common source of anchor failure.
The SwiveLock, by Arthrex, is a two part, screw-in knotless anchor. The tip of the anchor has an eyelet through which the suture legs are loaded. The tip is placed at the bottom of a hole drilled into the bone. The anchor is then screwed into the hole, securing the sutures in the bone hole. The suture ends are passed through the tissue from bottom to top above the anchor. These ends are then loaded into and secured in a knotless anchor implanted off the edge of the tissue. This construct does not provide a knot or other feature to press the tissue down against the bone above the screw-in anchor. A loss of tension in the strands passing between the screw-in and knotless anchors results in reduced compressive force of soft tissue to bone, which may significantly increase the likelihood of gap formation, leading to reduced healing and a compromised repair.
Any screw-in anchor preloaded with suture can be used in this manner. The anchor is placed, the sutures are passed through the tissue, and the free ends are secured in a knotless anchor off the lateral edge of the tissue. However, this construct does not provide compression above the anchor. The only compression on the tissue occurs beneath the suture passing between the anchors.
Smith & Nephew has marketed the KINSA knotless suture anchor. It is a PEEK anchor which is tapped into a pre-drilled hole in the bone. The anchor is preloaded with a loop of suture tied in a one-way sliding knot within the anchor body. The loop is passed through the tissue and the anchor is passed through the loop before inserting it into the bone tunnel. The sliding knot allows the surgeon to pull the free end of suture and tighten the loop through the tissue. This style of anchor is not preferred in the humeral head because of low pull-out forces, the requirement to pass suture prior to installing the anchor, and only 1 suture strand available for loading into a knotless anchor.